Date of this Version
Six ruminally and duodenally fistulated steers were fed three diets varying in source and concentration of dietary protein to determine impacts on ruminal metabolism, nutrient digestibility, and microbial crude protein (MCP) production as estimated by urinary purine derivative:creatinine (PD:C) ratio. Steers were fed a steam-flaked corn (SFC)-based diet with or without 1.5% urea, or a corn milling byproduct-based diet. Feeding a corn milling by-product-based diet resulted in greater ruminal pH and less time below ruminal pH 5.6, total tract OM digestibility, and ruminal propionate concentration when compared with either SFC-based treatment. The by-product-based treatment produced greater PD:C and MCP production values when compared with the SFC, no urea treatment. Responses in ruminal pH, MCP production, and PD:C indicate the by-product-based diet provided a more favorable rumen environment compared with SFC-based diets, and that urinary PD:C can be used to estimate differences in MCP production.